1. Field of the Invention
The present invention relates to a tuning circuit that extracts a signal corresponding to a predetermined channel form a television radio wave.
2. Description of the Related Art
A tuning circuit is used for extracting a band part corresponding to the selected channel from the television radio wave received by an antenna. The tuning circuit can extract a broadcast program by passing only a part synchronizing with the band of the selected channel.
In Patent documents 1 and 2, the tuning circuit using a superheterodyne method is disclosed as the tuning circuit. The tuning circuit using the superheterodyne method extracts a desired output signal by mixing the television radio wave with a local signal corresponding to the selected channel.
In the Patent documents, filters are provided before and after a mixing circuit and pass bands of the filters are fixed. Therefore, an input signal input from the antenna passes through the filter and then is mixed with the local signal by a mixer. Then, an output from the mixer is input to the filter, amplified by an amplifier, and output to a demodulation circuit as shown in Patent documents 1 and 2, for example.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2009-058485
[Patent Document 2] Japanese Patent Application Laid-Open No. 2009-016912
In some cases, noise can occur in the output signal due to an area where the broadcast program is watched, an environment where the antenna is installed in a house, and influence of radiation from peripheral devices. If the noise occurs in the output signal, noise images are generated on a screen output by an output device (e.g., display panel). This adversely affects viewing of the broadcast program.
The present invention provides a receiver that can improve a quality of the output signal.